It is known to tag petroleum fuels, such as gasoline, diesel fuel, heating oil, kerosene, etc. with markers, as for example, as taught in U.S. Pat. No. 5,205,840.
A dye is defined herein as a material lending visible color when dissolved in the dyed fuel. Examples of dyes which have been used for dyeing organic liquids are Color Index Solvent Red #24, Solvent Red #19, Solvent Yellow #14, Solvent Blue #36, and Solvent Green #3.
A marker is defined herein as a substance which can be dissolved in a liquid to be identified, then subsequently detected by performing a simple chemical or physical test on the tagged liquid. Markers that have been proposed, or are in use, include furfural, quinizarin, diphenylamine and radioactive materials. (Radioactive materials have not been accepted in Western countries because of special equipment and precautionary measures associated with their handling.)
Dyes and markers are needed to clearly distinguish chemically or physically similar liquids. As one example, fuels are dyed or tagged to provide visually distinctive brand and grade denominations for commercial and safety reasons. As another example, some lightly taxed fuels are dyed or tagged to distinguish them from similar materials subject to higher taxes. Furthermore, certain fuels are dyed or tagged to deter fraudulent adulteration of premium grade fuels with lower grade fuels, such as by blending kerosene, stove oil, or diesel fuel into regular grade gasoline or blending regular grade gasoline into premium grade gasoline. Identification of particular batches of bulk liquids for protection against theft is another valuable function of markers and dyes, particularly for identifying fuels owned by large government, military or commercial consumers. Finally, marketers of brand name fuels dye or tag their fuels to detect substitution of others fuels in their distribution system.
Dyes alone are not always adequate to securely and reliably identify liquids. Many dyes are easily removed by unauthorized persons. Furthermore, dyes can be obscured by other natural or added substances (particularly dyes present at low concentrations in a mixture of fuels). Because dyes alone have these shortcomings, a combination of a dye and a marker often is used to tag an organic liquid.
Above-referenced U.S. Pat. No. 5,156,653 recites important characteristics of certain desirable markers for petroleum include:
1. are entirely foreign to the liquids; PA1 2. can be supplied as highly concentrated solutions in petroleum-compatible solvents; PA1 3. are easily detected by a simple field test; PA1 4. are not obscured by unstable natural components of the liquids; PA1 5. are stable over the anticipated storage life of the tagged liquid (usually three to six months); and PA1 6. have identities which can be confirmed by laboratory methods.
The dyes of the present invention fulfil requirements of 1-6 above. The markers of the present invention are "silent" in that at the levels at which they are used, they provide substantially no color to the petroleum fuel, but undergo a reaction during a detection procedure. The silent nature of the markers of the present invention make them particularly suitable as markers in non-dyed petroleum fuels, but they are suitable in dyed petroleum fuels, as well, where the markers do not alter the color imparted by the dyes. The silent nature of the markers of the present invention also is advantageous in that they cannot be detected without an appropriate reactive extraction system, making misuse or dilution of a petroleum fuel mixed with a marker of the present invention more difficult.
A suitable petroleum marker that is to be extracted by a petroleum-immiscible solution must meet somewhat demanding solubility requirements. In the final product, the marker is only present in the petroleum fuel in parts-per-million quantities, but the marker is desirably provided to the petroleum in concentrated form, either in a petroleum fuel or in a petroleum-miscible solvent. On the other hand, a small amount of extractant should remove substantially all of the marker from the specimen of petroleum fuel being tested.
The markers of the present invention are detectable by extraction from the petroleum fuel with a dilute acidic solution, e.g., a 10% HCl or formic acid solution. It is desirable that acid-extractable markers be available, particularly markers which develop a color sufficiently strong to be clearly differentiated from any background color which might develop from acid reaction with petroleum impurities or develop a color which is sufficiently different from any such background color.
Acid-extractable markers in use today suffer significantly from the fact that they require the use of concentrated mineral acids to extract, resulting in very significant interference from extracted background color.
Having acid-extractable markers increases the variety of materials with which petroleum might be marked. As most present day markers are base-extractable, someone intent on mislabeling petroleum fuel might first check for marker by extraction with base, thereby missing an acid-extractable marker. Also, acid-extractable markers may provide for a double marking system, including both the acid-extractable marker and a base-extractable marker. Likewise, the impermissible mixing of two petroleum fuels each tagged with base-extractable markers might be missed, particularly if the developed marker colors is similar; whereas, impermissible mixing a petroleum fuel tagged with an acid-extractcable marker and a petroleum fuel tagged with a base-extractable marker can be detected by subsequent extractions with acid and base.
Markers of the present invention are also advantageous in that they provide relatively quantitative determinations. Most markers are adequate for detection of their presence in petroleum fuel; however, many available markers, especially acid-extractable markers, do not provide a good quantitative measurement of their levels in liquid petroleum fuels. Quantitative determinations are particularly important in cases where dilution is suspected, e.g., dilution of a higher-taxed fuel with a lower-taxed fuel.